Optical displacement sensor employing reflected light of four wa

Details Optical displacement sensor employing reflected light of four wa Optical displacement sensor employing reflected light of four wa

1994-03-02

1995-05-23

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

25022723, H01J 516, H01J 4014

Patent

active

054183618

ABSTRACT:
An optical displacement sensor suitable for use in drowned environments where the refractive index of a medium in the optical path may vary, comprises a light source emitting first to fourth wavelengths. The first and second wavelengths are within the infrared region of the spectrum, whereas the third and fourth wavelengths are in the visible region of the spectrum. A zone plate focuses the first and second wavelengths to respective positions substantially at the extremes of movement of a reflective element whose position is to be measured. The zone plate also focuses the third and fourth wavelengths to respective positions. A cold mirror is interposed between the zone plate and the reflective element and is arranged to transmit the first and second wavelengths and to reflect the third and fourth wavelengths. The ratio of the intensities of the light reflected from the cold mirror gives information about the refractive index of the medium in the optical path. This information can be used to correct the measurement of the position of the reflective element which is determined by the ratio of reflected intensities of the first and second wavelengths.

REFERENCES:
patent: 4778988 (1988-10-01), Henderson
patent: 4798951 (1989-01-01), Walker
patent: 4946275 (1990-08-01), Bartholomew
patent: 5001338 (1991-03-01), Boero
patent: 5017772 (1991-05-01), Hafle
patent: 5068527 (1991-11-01), Iwamoto et al.
patent: 5164600 (1992-11-01), Das et al.

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